Cranial ct-based grading method and system

ABSTRACT

Disclosed are a cranial CT-based grading method and a corresponding system, which relate to the field of medical imaging. The cranial CT-based grading method as disclosed solves the problems of relatively great subjective disparities and poor operability in eye-balling ASPECTS assessment. The grading method includes: determining frames where target image slices are located from to-be-processed multi-frame cranial CT data; extracting target areas; performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area; and outputting a grading outcome based on infarct judgment outcomes regarding all target areas. The grading method and system as disclosed may eliminate or mitigate the diagnosis disparities caused by human factors and imaging deviations due to different imaging devices, and shorten the time taken by human observation, consideration, and bared-eye grading, thereby serving as a computer-aided method to provide reference for medical studies on stoke.

FIELD

The present disclosure relates to the field of medical imaging and computer technologies, and more particularly relates to a cranial CT-based grading method and a corresponding system.

BACKGROUND

ASPECTS (Alberta Stroke Program Early CT Score), proposed by Barber et al. in 2000, offers a significant basis for stroke diagnosis and treatment. According to the ASPECTS grading method, the middle-cerebral-artery (MCA) territory of an acute stroke patient is divided into 10 areas of interest based on his or her cranial CT data, including: C—Caudate head; L—lentiform nucleus, IC—internal capsule Post Limb, I—insular ribbon, M1—anterior MCA cortex, M2—MCA cortex lateral to insular ribbon, M3—posterior MCA cortex, which are located at the ganglionic level, and M4—anterior MCA territory immediately superior to M1, M5—lateral MCA territory immediately superior to M2, and M6—posterior MCA territory immediately superior to M3, which are located at the supraganglionic level. The above 10 areas are allotted the same weight, i.e., 1 point for each area, such that the total ASPECTS value is 10 points. A value resulting from subtracting the number of areas with early ischemic changes from the total score serves as the grading outcome, offering a reference for disease diagnosis and treatment. The above grading method mainly addresses anterior circulation. With further in-depth studies on stroke, Puetz et al. proposed PC-ASPECTS (Posterior Circulation Acute Stroke Prognosis Early CT Score) in 2008. The PC-ASPECTS grading method mainly scores the bilateral thalami, the bilateral cerebella, the bilateral posterior cerebral artery (PCA) territories, the midbrain, and the pons, wherein a 1-point weight is allotted to each of the bilateral thalami, bilateral cerebella, bilateral posterior cerebral artery (PCA) territories, and a 2-point weight is allotted to each of the midbrain and pons; as such, the total PC-ASPECTS value is 10 points. A value resulting from subtracting the weighted points corresponding to the areas with early ischemic changes from the total score serves as the grading outcome, offering a reference for disease diagnosis and treatment.

In current clinical applications, irrespective of the anterior-circulation ASPECTS measurement or the posterior-circulation ASPECTS measurement, they mainly rely on eye-balling assessment. However, due to factors such as different imaging equipment, different clinicians, and different patient conditions, the agreement between interpretations of the cranial CT cannot be guaranteed, such that eye-balling assessment of ASPECTS will lead to a great subjective disparity. Therefore, such “eye-balling assessment” approach has a poor operability. On the other hand, the stroke condition develops very rapidly, and blood supply interruption of over 4 or 5 minutes would cause permanent and irreversible infarct, resulting in a very high dependence/death rate; further, the boundaries of tissue partitions on the CT are difficult to discern, such that if the partitions cannot be determined quickly and accurately, diagnosis and treatment will be delayed.

Therefore, a grading method is currently desired, which may eliminate or mitigate diagnosis disparities caused by human factors including technical level, operating technique, imaging quality, human eye discernibility, fatigue degree, and different cognitive experience, as well as the diagnosis disparities caused by imaging deviations between different imaging equipment, and shorten the time taken by human observation, consideration, and eye-balling grading, so as to serve as a computer-aided method to provide objective references for medical studies on stroke.

SUMMARY

Embodiments of the present disclosure provide a cranial CT-based grading method and a corresponding system so as to eliminate or mitigate diagnosis disparities due to subjective factors and objective factors such as imaging deviations between different image equipment, shorten the time taken by grading, and enhance diagnosis efficiency and accuracy.

An embodiment of the present disclosure provides a cranial CT-based grading method, comprising steps of:

determining frames where target image slices are located from to-be-processed multi-frame cranial CT data, wherein the target image slices refer to the slices, where the cranial CT data for being graded are located, in the cranial CT;

extracting target areas based on the frames where the target image slices are located, wherein the target areas refer to areas for being graded in the cranial CT data;

performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area; and

outputting a grading outcome based on infarct judgment outcomes regarding all target areas.

Preferably, the determining frames where target image slices are located from to-be-processed multi-frame cranial CT data specifically comprises:

extracting image features of the to-be-processed multi-frame cranial CT data, and determining distances from respective frames of cranial CT data in the multi-frame cranial CT data to respective target image slices; and

determining the frames where the target image slices are located based on the distances from the respective frames of cranial CT data to the respective target image slices.

Preferably, the extracting target areas based on the frames where the target image slices are located specifically comprises:

classifying each pixel point in the cranial CT data using digital labels based on the frames where the target image slices are located and outputting a two-dimensional matrix with digital labels corresponding to respective pixel points in the frames where the target image slices are located, wherein the digital labels are in one-to-one correspondence with the target areas, and the two-dimensional matrix is in correspondence with the frames where the target image slices are located.

Preferably, the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area specifically comprises:

performing infarct judgment on each pixel point included in the target area to output an infarct judgment outcome regarding the target area.

Further, the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area further comprises:

judging, based on the infarct judgment outcome regarding the target area, whether infarct is indicated in the target areas in both left and right cerebral hemispheres; and

if infarct is indicated in the target areas in both left and right cerebral hemispheres, further determining which specific side is infarcted, and correcting the infarct judgment outcome regarding the target area as an update infarct judgment outcome regarding the target area.

Preferably, the outputting a grading outcome based on infarct judgment outcomes regarding all target areas specifically comprises:

determining all infarcted target areas based on the infarct judgment outcomes regarding all target areas;

subtracting, based on weights allotted to respective target areas, weights of the infarcted target areas from the total score to output a resulting value as the grading outcome.

An embodiment of the present disclosure provides a cranial CT-based grading system, comprising:

an area extracting module configured for extracting target areas from to-be-processed multi-frame cranial CT data, wherein the target areas refer to areas for being graded in the cranial CT data;

an infarct identifying module configured for performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area; and

a grading module configured for outputting a grading outcome based on infarct judgment outcomes regarding all target areas.

Preferably, the extracting target areas from to-be-processed multi-frame cranial CT data specifically comprises:

determining frames where target image slices are located from the to-be-processed multi-frame cranial CT data, respectively, wherein the target image slices refer to the slices, where the cranial CT data for being graded are located, in the cranial CT; and

extracting the target areas based on the frames where the target image slices are located, wherein the target areas refer to areas for being graded in the cranial CT data.

Preferably, the determining frames where target image slices are located from the to-be-processed multi-frame cranial CT data specifically comprises:

extracting image features of the to-be-processed multi-frame cranial CT data, and determining distances from respective frames of cranial CT data in the multi-frame cranial CT data to respective target image slices; and

determining the frames where the target image slices are located based on the distances from the respective frames of cranial CT data to the respective target image slices.

Preferably, the extracting the target areas based on the frames where the target image slices are located specifically comprises:

classifying each pixel point in the cranial CT data using digital labels based on the frames where the target image slices are located and outputting a two-dimensional matrix with digital labels corresponding to respective pixel points in the frames where the target image slices are located, wherein the digital labels are in one-to-one correspondence with the target areas, and the two-dimensional matrix is in correspondence with the frames where the target image slices are located.

Preferably, the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area specifically comprises:

performing infarct judgment on each pixel point included in the target area to output an infarct judgment outcome regarding the target area.

Further, the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area further comprises:

judging, based on the infarct judgment outcome regarding the target area, whether infarct is indicated in the target area in both left and right cerebral hemispheres; and

if infarct is indicated in the target area in both left and right cerebral hemispheres, further determining which specific side is infarcted, and correcting the infarct judgment outcome regarding the target area as an updated infarct judgment outcome regarding the target area.

Preferably, the outputting a grading outcome based on infarct judgment outcomes regarding all target areas specifically comprises:

determining all infarcted target areas based on the infarct judgment outcomes regarding all target areas; and;

subtracting, based on weights allotted to respective target areas, weights of the infarcted target areas from the total score to output a resulting value as the grading outcome.

At least one of the technical solutions above adopted in the embodiments of the present disclosure may achieve the following beneficial effects:

By means of extracting target areas from to-be-processed multi-frame cranial CT data to perform infarct judgment on the respective target areas and then outputting a grading outcome, the embodiments of the present disclosure may eliminate or mitigate the diagnosis disparities caused by human factors as well as the diagnosis disparities caused by imaging deviations between different imaging equipment, and shorten the time taken by human observation, consideration, and eye-balling grading, so as to serve as a computer-aided method to enhance diagnosis efficiency and accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

To elucidate the technical solutions of the present disclosure or the technical solutions in the prior art, the drawings used in describing the embodiments of the present disclosure or the prior art will be briefly introduced below. It is understood that the drawings as described only relate to some embodiments of the present disclosure. To those skilled in the art, other drawings may be derived based on these drawings without exercise of inventive work, wherein:

FIG. 1 is an outline diagram of a cranial CT-based grading method according to an embodiment of the present disclosure;

FIG. 2a is a schematic diagram of applying ASPECTS grading to the ganglionic level according to an embodiment of the present disclosure;

FIG. 2b is a schematic diagram of applying ASPECTS grading to the supraganglionic level according to an embodiment of the present disclosure;

FIG. 3a is a schematic diagram of pons and bilateral cerebellar areas subjected to PC-ASPECTS grading according to an embodiment of the present disclosure;

FIG. 3b is a schematic diagram of the midbrain area subjected to PC-ASPECTS grading according to an embodiment of the present disclosure;

FIG. 3c is a schematic diagram of the bilateral thalami and bilateral PCA-territories subjected to PC-ASPECTS grading according to an embodiment of the present disclosure;

FIG. 4 is a flow diagram of a cranial CT-based grading method according to an embodiment of the present disclosure;

FIG. 5 shows a schematic diagram of determining the frames where the ganglionic level and the supraganglionic level are located according to an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of performing infarct judgment according to an embodiment of the present disclosure; and

FIG. 7 is a schematic diagram of a cranial CT-based grading system according to an embodiment of the present disclosure;

NOTES

In FIG. 3a , pons and bilateral cerebella from top to down;

In FIG. 3c , bilateral thalami and bilateral PCA-territories from top to down;

In FIG. 3, the numbers 1 and 2 represent the weights of respective areas.

DETAILED DESCRIPTION OF EMBODIMENTS

To facilitate those skilled in the art to understand, the technical solutions of the present disclosure will be described in a clear and comprehensive manner with reference to the accompanying drawings; it is apparent that the embodiments described herein are only part of the embodiments of the present disclosure, rather all of them. All other embodiments obtained by those skilled in the art without exercise of inventive work based on the embodiments in the present disclosure shall fall within the protection scope of the present disclosure.

FIG. 1 is a frame diagram of a cranial CT-based grading method according to an embodiment of the present disclosure, specifically comprising steps of:

Step 101: determining frames where target image slices are located from to-be-processed multi-frame cranial CT data, respectively.

A CT is made up of a certain number of pixel points with different greyscales from black to white in a matrix arrangement. A CT number is a measurement of intensity of a corresponding human body tissue. As a single frame of CT is a sectional (typically cross-section) image with a certain thickness, a plurality of continuous sectional images are needed to display an entire organ. Therefore, when performing ASPECTS assessment, a series of multi-frame images need to be observed for giving assessment; in this embodiment, the to-be-processed cranial CT data all have multiple frames.

In an embodiment of the present disclosure, the 10 areas subjected to anterior-circulation ASPECTS assessment are respectively located at the ganglionic level and the supraganglionic level, as specifically shown in FIG. 2. Therefore, when performing anterior-circulation ASPECTS assessment, it is needed to first determine the frames where the ganglionic level and the supraganglionic level are located in the to-be-processed multi-frame cranial CT data, wherein the target image slices refer to the ganglionic level and the supraganglionic level.

In another embodiment of the present disclosure, among the 8 areas for posterior-circulation ASPECTS assessment, the pons and bilateral cerebella are located in the cerebellar territory, the midbrain is located in the midbrain territory, and the bilateral thalami and the bilateral PCA-territories are located in the cerebral territory, as specifically shown in FIG. 3. Therefore, when performing posterior-circulation ASPECTS assessment, it is needed to first determine the frames where the cerebellar territory, the midbrain territory, and the cerebral territory are located from the to-be-processed multi-frame cranial CT data, wherein the target image slices refer to the cerebella territory, the midbrain territory, and the cerebral territory.

Step S103: extracting target areas.

After determining the frames where the target image slices are located in step S101, it is needed to further analyze the image data of the frames where the target image slices are located so as to determine whether respective pixel points on the frames belong to the target areas and to which specific areas in the target areas they belong; the target areas herein refer to the areas for being graded in the frames where the target image slices are located, and by judging cerebral infarct in the target areas, the cranial CT may be graded. In an embodiment of the present disclosure, the target areas may refer to the caudate heads, lentiform nuclei, internal capsules Post Limb, insular ribbons, and M1-M6 areas in the left and right cerebral hemispheres, wherein there are 20 areas in total. In another embodiment of the present disclosure, the target areas may refer to the pons, bilateral cerebella, midbrain, bilateral thalami, and bilateral PCA-territories, wherein there are 8 areas in total. When a pixel point does not belong to any of the target areas, it is judged to belong to the background area.

Step S105: performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area.

After extracting the target areas in step S103, it is needed to further analyze and judge which areas are infarcted. In a CT, one CT number corresponds to one greyscale. Infarct may be determined in a plurality of manners. An exemplary manner is based on the symmetric property of human brains: the CT numbers of normal human brain tissues at symmetrical positions in the left and right cerebral hemispheres are substantially identical, i.e., their greyscale values are substantially identical. However, if a brain tissue at one side is infarcted, its greyscale value will decline; therefore, by comparing with the greyscales of the corresponding areas in the contralateral hemisphere, the areas of infarct may be determined, thereby implementing infarct judgment on respective target areas included in the target areas.

Besides the approach indicated above, another exemplary manner of infarct judgment is to first extract features, e.g., greyscale information, greyscale information of a neighboring pixel point, gradient information, and gradient information of the neighboring pixel point, etc., and then train a model by supervised learning, which may also implement infarct judgment.

In normal circumstances, when the cerebral infarct occurs, it occurs only to one side; if it occurs to both sides, the cerebral tissues are possibly already dead. Therefore, if the infarct judgment outcome regarding the target area shows presence of early ischemia changes in both left and right cerebral hemispheres, the infarct judgment outcome of a certain side might be caused by noises such as image artifacts. Based on the above reasons, if the infarct judgment outcome shows presence of early ischemia changes in both left and right cerebral hemispheres, it is needed to further determine which specific side is infarcted so as to correct the infarct judgment outcome. Upon correction, the judgment may be made based on greyscale variations. For bilateral target areas, the smaller the ratio between bilateral greyscales, or the smaller the difference between bilateral greyscales, or the smaller the numerical value resulting from the combination of the ratio and the difference, the higher the confidence is; therefore, by comparing the minimum values among the ratios between bilateral greyscales, or the minimum differences between bilateral greyscales, or the minimum numerical values resulting from the combinations of the ratios and the differences in the bilateral target areas, the side with the smaller value, i.e., the side with a higher confidence, is determined to be infarcted, while the contralateral hemisphere is determined as not infarcted; the above outputted infarct judgment outcome is then corrected based on the confidence outcome.

Step S107: outputting a grading outcome based on infarct judgment outcomes regarding all target areas.

In normal circumstances, the total scores of the anterior-circulation ASPECTS and the posterior-circulation ASPECTS are both 10 points; when infarct occurs, the ASPECTS value will decline. Based on the determined infarct judgment outcome, the score obtained by subtracting the points of infarcted areas from the 10 points based on the weights allotted to respective target areas is the final score, thereby implementing grading of the cranial CT.

Grading the cranial CT by the method provided in this embodiment may eliminate or mitigate diagnosis disparities caused by human factors as well as the diagnosis disparities caused by imaging deviations between different imaging equipment, which greatly reduces the time taken by human observation and consideration.

To further illustrate the cranial CT-based grading method, FIG. 4 is a flow diagram of a cranial CT-based grading method according to an embodiment of the present disclosure, wherein the grading process is illustrated in detail with the anterior-circulation ASPECTS as an example.

Step 5401: obtaining to-be-processed cranial CT data.

In a CT, different pixel sizes result in correspondingly different numbers of pixels. For example, the pixel size may be 1.0 mm*1.0 mm or 0.5 mm*0.5 mm, and the corresponding number of pixels may be 256*256 or 512*512. Apparently, the smaller the pixel size, the larger the number of pixels, and the higher the spatial resolution. As the CT data is a sectional image, a plurality of continuous sectional images are needed to display an entire organ; therefore, the to-be-processed cranial CT has multiple frames.

Step S403: determining the frames where the ganglionic level and the supraganglionic level are located.

Among the to-be-processed multi-frame cranial CT data, the frames of interest are those where the ganglionic level and the supraganglionic level are located, which need to be first determined. A feature of a certain frame of image may be extracted using the neural network or other algorithms, wherein the feature may be the greyscale of the image, e.g., the M area (M1-M6 areas are collectively referred to as the M area) is located at the cerebral cortex which is mainly made up of grey matter with a greyscale value of about 35; the feature may also be the shape of the image, e.g., the lentiform nucleus has a lentiform shape, and the insular ribbon has a ribbon shape, whose greyscales are generally different from the surrounding; the feature of the image may also be texture information, e.g., the M area generally has sulci and gyri; the location information may also be extracted as a feature, e.g., the insular ribbon abuts the M area, and the M area adjoins the skull. Then, the distances from this frame of image to the ganglionic level and to the supraganglionic level are estimated to determine its position in the cerebrum; as such, the frames where the ganglionic level and the supraganglionic level are located may be further determined.

FIG. 5 shows a schematic diagram of the distances from respective frames of the CT to the ganglionic level and to the supraganglionic level according to an embodiment of the present disclosure. Specifically, an image sequence has 12 frames in total with an inter-slice gap of 10 mm. The distances from the respective frames to the ganglionic level and to the supraganglionic level are computed using the neural network or other algorithms, as shown in FIG. 5. It may be seen from FIG. 5 that the 5^(th) frame is closest to the ganglionic level, and the 7^(th) frame is closest to the supraganglionic level; therefore, the 5^(th) frame belongs to the ganglionic level and the 7^(th) frame belongs to the supraganglionic level. The distances from respective frames of the CT data to the ganglionic level and to the supraganglionic level may be determined by MSE (mean square error) or by MAE (mean absolute error) or other similar algorithms, which may also be applied to determine the frames where the ganglionic level and the supraganglionic level are located; other similar algorithms are all regarded as equivalent algorithms.

In an embodiment of the present disclosure, the ganglionic level and the supraganglionic level in the CT scan sequence are manually labeled, and a trained model is obtained by supervised learning to classify the ganglionic level and the supraganglionic level, outputting [P1, P2, P3], wherein P1 denotes the probability of neither belonging to the ganglionic level nor belonging to the supraganglionic level, P2 denotes the probability of belonging to the ganglionic level, and P3 denotes the probability of belonging to the supraganglionic level, wherein P1+P2+P3=1. When n frames of CT data are inputted, a n*3 matrix is outputted; if the value of P2 in the k^(th) row is the largest, the value of P3 in the p^(th) row is the largest; then, it is believed that the k^(th) frame is at the ganglionic level, and the p^(th) frame is at the supraganglionic level. This approach may also be applied to determine the frames where the ganglionic level and the supraganglionic level are located.

Step S405: extracting the target areas in the left and right cerebral hemispheres based on the frames where the ganglionic level and the supraganglionic level are located.

To extract the target areas in the left and right hemispheres, it is needed to classify, using digital labels, each pixel point in the frames where the ganglionic level and the supraganglionic level are located so as to determine to which specific area the pixel point belongs in the target areas in the left and right cerebral hemispheres. In an embodiment of the present disclosure, 0 represents the background, 1, represents the left M1, 2 represents the left M2, 3 represents the left M3, 4 represents the left caudate head, 5 represents the left insular ribbon, 6 represents the left internal capsule Post Limb, 7 represents the left lentiform nucleus, 8 represents the right M1, 9 represents the right M2, 10 represents the right M3, 11 represents the right caudate head, 12 represents the right insular ribbon, 13 represents the right internal capsule Post Limb, 14 represents the right lentiform nucleus, 15 represents the left M4, 16 represents M5, 17 represents the left M6, 18 represents the right M4, 19 represents the right M5, and 20 represents the right M6. An image of the frames where the ganglionic level and the supraganglionic level are located is subjected to the neural network or other algorithms to output a two-dimensional matrix with a digital label, wherein the values in the matrix are 0˜20, among which, 1-20 represent target areas. If the input data is a 512*512 image, a two-dimensional matrix with a digital label 512*512 will be outputted. The two-dimensional matrix is in correspondence with the frames where the ganglionic level and the supraganglionic level are located. The digital labels in the two-dimensional matrix corresponding to the frame where the ganglionic level is located are 0˜14, and the digital labels in the two-dimensional matrix corresponding to the frame where the supraganglionic level is located are 0, and 15˜20. Based on the two-dimensional matrix, the areas to which respective pixel points in the frames belong may be determined.

Step S407: performing infarct judgment on bilaterally corresponding target areas in the left and right cerebral hemisphere target areas.

A CT number is a measurement of relative intensity in a CT, a unit of which is Housefield Unit (HU); CT numbers of human tissues have fixed ranges. For example, the CT number of water is 0; the CT number of blood ranges from 60 to 100 HU, the CT number of grey matter ranges from 30 to 35 HU, the CT number of white matter ranges from 20 to 25 HU, the CT number of muscles ranges from 20 to 40 HU, and the CT number of bones is greater than 1000 HU. In a CT, one CT number corresponds to one greyscale. Due to the symmetrical property of human brains, in normal conditions, the mean CT numbers of human brain tissues at symmetrical positions in the left and right cerebral hemispheres are substantially identical, i.e., their greyscale values are substantially identical. However, if the brain tissues at one side are infarcted, their greyscale value will decline; therefore, by comparing with the greyscale of the corresponding area in the contralateral hemisphere, an infarcted area may be determined.

Based on the digital labels outputted in step S405, symmetrical target areas in the left and right cerebral hemispheres in the CT are located; all pixel points in the target areas are traversed; meanwhile, to eliminate interference such as noises, thresholds thre0 and thre1 are set; the pixel points with greyscale values between thre0 and thre1 are selected, wherein thre0 may be set to 30 HU and thre1 may be set to 50 HU. The greyscale values of all eligible pixel points in one target area are summed and then averaged, wherein the average value serves as the average greyscale value of the target area; by comparison between the greyscale value of the target area at one side with the greyscale value of the contralateral target area, whether the target area is infarcted may be determined.

In an embodiment of the present disclosure, infarct judgment may be made by extracting image features. Specifically, image features, such as greyscale information, greyscale information of a neighboring pixel point, gradient information, and gradient information of the neighboring pixel point, are extracted and manually labelled and then trained by supervised learning such as SVM (Support Vector Machine) and random forest, etc. With the trained model, image features of each pixel point in the image are extracted to obtain the infarct judgment outcome regarding said each pixel point. Specifically, with this approach, the outputted infarct judgment outcomes are dichotomic, i.e., 0 indicates not infarcted, and 1 indicates infarcted.

FIG. 6 is a schematic diagram of infarct judgment according to an embodiment of the present disclosure. Specifically, the judgment may be made by a difference algorithm, a ratio algorithm, and a combination of the ratio algorithm and the difference algorithm; any other algorithms of infarct judgment based on greyscale changes are regarded as equivalents to the algorithms adopted in the present disclosure. For example, to determine whether a lentiform nucleus is infarcted, a point (with the digital label 7) in the left lentiform nucleus and a point (with the digital label 14) in the right lentiform nucleus in the image data are located; all pixel points corresponding to the digital label 7 and the digital label 14 are traversed to respectively screen pixel points with a greyscale value between 30 HU and 50 HU among the pixel points with the digital label 7 and the digital label 14. With the screened pixel points with the digital label 7 and the digital label 14, the mean value of the greyscale values of the pixel points with the digital label 7 is computed as the greyscale value for the left lentiform nucleus; the mean value of the greyscale values of the pixel points with the digital label 14 is computed as the greyscale value for the right lentiform nucleus; the greyscale value of the left lentiform nucleus and the greyscale value of the right lentiform nucleus are then compared to determine whether there is an infarcted lentiform nucleus and the lentiform nucleus at which side is infarcted. Other algorithms of computing the mean greyscale value, e.g., subjecting the greyscale value of each pixel point to certain operation and conversion, e.g., greyscale stretch, are all regarded as equivalent to the algorithms adopted in the present disclosure.

In an embodiment of the present disclosure, infarct judgment is made using a difference algorithm; it is believed that in corresponding target areas in the left and right cerebral hemispheres, if the difference between the greyscale value of a certain target area at one side and the greyscale value of the contralateral target area is less than a preset threshold cliff, a corresponding area in the cranial CT is believed to be infarcted, wherein the side with the lower greyscale value is the infarcted side. Generally, the threshold duff is −2. For example, in the embodiment shown in FIG. 5, the difference between the greyscale value of the left M2 area and the greyscale value of the right M2 area is −2.7, less than the threshold −2; then, it is believed that the left M2 area is infarcted. With the same algorithm, it is determined that the left M3 and the right M4 are infarcted.

In an embodiment of the present disclosure, infarct judgment is made using a ratio algorithm; it is believed that in corresponding target areas in the left and right cerebral hemispheres, if the ratio value between the greyscale value of a target area at one side and the greyscale value of the contralateral target area is less than a preset threshold ratio, a corresponding area in the cranial CT is infarcted, wherein the side with the lower greyscale value is the infarcted side. Generally, the threshold ratio is 0.96. For example, in the embodiment of FIG. 6, the ratio between the left lentiform nucleus and the right-side lentiform nucleus is 0.99, greater than 0.96; then, it is believed that the lentiform nuclei are not infarcted, in agreement with the judgment outcome of the difference algorithm. The ratio between the greyscale value of the left M2 area and the greyscale value of the right M2 area is 0.92, less than 0.96; then it is believed that the left M2 area is infarcted. With the same algorithm, it is determined that the left M3 is infarcted.

In an embodiment of the present disclosure, infarct judgment is made by an algorithm combining the ratio algorithm and the difference algorithm. It is believed that the basis for infarct is ratio <0.96 and difference ←2. In the embodiment of FIG. 6, this approach is adopted to perform infarct judgment on the target areas in the cranial CT, wherein the left M2, M3 and the right M4 are infarcted. The basis for infarct judgment may also be ratio <0.96 or difference ←2. In the embodiment of FIG. 6, the same approach is adopted to perform infarct judgment, wherein the left M2 and M3 are infarcted.

Generally, the CT number of a tissue with early ischemia change is not lower than 20 HU; supposing that the cerebral tissues of a target area at the contralateral hemisphere are not infarcted, which have a mean greyscale value of about 40 Hu, then the ratio between the greyscales of the bilateral target areas cannot be less than 0.5 and the absolute value of the difference duff cannot be greater than 20. In an embodiment of the present disclosure, c=(ratio−0.5)/0.7+(diff+20)/50 may be adopted to perform infarct judgment on a target area in the cranial CT; if the value is less than or equal to 1, it is believed that the cerebral tissue in the target area at that side is infarcted; if greater than 1, not infarcted. In the embodiment of FIG. 6, the difference of the right M4 area is −1.6 and the ratio is 0.95; (0.95−0.5)/0.7+(−1.6+20)/50=1.02>1, then it is believed that the M4 area is not infarcted. With this algorithm, the left M2 and M3 areas are determined to be infarcted.

After infarct judgment is completely done to the to-be-processed multi-frame cranial CT data, the infarct judgment outcomes regarding 20 target areas are outputted for subsequent grading. The infarct judgment outcomes above are each represented by an array including three elements. The first element of the array is a Boolean data type, wherein 0 represents not infarcted, and 1 represents infarcted; the second element is a floating-point number, which is the result of dividing the mean greyscale value of a certain target area at the present side by the mean greyscale value of the contralateral target area; the third element is a floating-point number, which is the result of the mean grey scale value of the target area at the present side minus the mean greyscale value of the contralateral target area. For example, the first output is [0, 1, 0], wherein 0 indicates that the left M1 area is not infarcted, the mean greyscale value of the left M1 area divided by the mean greyscale value of the right M1 area is 1, and the mean greyscale value of the left M1 territory minus the mean greyscale value of the right M1 area is 0.

Step S409: performing denoising processing to the infarcted pixel points in the target areas in the left and right cerebral hemispheres.

Respective pixel points in the target areas have been classified in step S407. Isolated infarcted pixel points might be existent among the pixel points of these areas. Such isolated infarcted pixel points are possibly caused by factors such as imaging quality and imaging equipment, which belong to interference noises; therefore, it is needed to remove these noises to prevent affecting the subsequent grading.

The infarct judgment outcomes with removal of isolated pixel points need to be corrected. If an infarct judgment outcome in step 405 is [1, 1], it is found, using the connected region denoising method, that the pixel point is an isolated pixel point, then it is determined that the pixel point is not infarcted; therefore, the infarct judgment outcome in step S405 is corrected to [1, 0].

Step S411: further judging the infarct judgment outcomes regarding all target areas in the left and right cerebral hemispheres.

The infarct judgment outcomes regarding the 20 target areas outputted in step S409 possibly have a scenario that an early ischemia change is present in bilateral target areas. In normal circumstances, there should be only one side infarcted; if the early ischemia change is present at both sides, it needs to further determine which specific side is infarcted. The judgment may be made based on the principle that the side with the smaller greyscale change has a higher probability of infarct. For bilateral target areas in the left and right cerebral hemispheres, the smaller the ratio between bilateral greyscales, or the smaller the difference between bilateral greyscales, or the smaller the numerical value resulting from the combination of the ratio and the difference, the higher the confidence is; therefore, by comparing the minimum values among the ratios between bilateral greyscales, or the minimum differences between bilateral greyscales, or the minimum numerical values resulting from the combinations of the ratios and the differences in the target areas, the side with the smaller value, i.e., the side with a higher confidence, is determined to be infarcted, while the contralateral hemisphere is determined as not infarcted; the above outputted infarct judgment outcomes are then corrected based on the infarct judgment outcomes outputted in step S409.

Based on the algorithm described in step S409, the embodiment shown in FIG. 6 is subjected to infarct judgment using the ratio algorithm or the difference value algorithm; then, the outputted infarct judgment outcomes for target areas 1-20 are provided below: 1: [0, 0.99, −0.5], 2: [1, 0.92, −2.7], 3: [1, 0.93, −2.4], 4: [0, 1, 0], 5: [0, 1.01, 0.2], 6: [0, 1.03, 0.9], 7: [0, 0.99, −0.5], 8: [0, 1.02, 0.5], 9: [0, 1.09, 2.7], 10: [0, 1.08, 2.4], 11: [0, 1, 0], 12: [0, 0.99, −0.2], 13: [0, 0.97, −0.9], 14: [0, 1.01, 0.5], 15: [0, 1.05, 1.6], 16: [0, 1, 0], 17: [0, 1, 0], 18: [1, 0.95, −1.6], 19: [0, 1, 0], 20: [0, 1, 0].

In an embodiment of the present disclosure, the above outputted infarct judgment outcomes are subjected to further judgment based on the ratio-based confidence algorithm, wherein the minimum ratio in the left target areas is 0.92, and the minimum ratio in the right target areas is 0.95. Following the principle that the side with the smaller ratio has a higher confidence and is infarcted, the left side is infarcted. Further, the outputted infarct judgment outcome is corrected as such: correcting 18: [1, 0.95, −1.6] to 18: [0, 0.95, −1.6]; while the remained infarct judgment outcomes do not change; then the corrected infarct judgment outcomes regarding all target areas in the left and right cerebral hemispheres serve as updated infarct judgment outcomes for subsequent grading.

In an embodiment of the present disclosure, the above outputted infarct judgment outcomes are subjected to further judgment based on the difference-based confidence algorithm, wherein the minimum difference in the left target areas is −2.7, and the minimum difference in the right target areas is −1.6. following the principle that the side with the smaller difference has a higher confidence and is thus infarcted, due to −2.7←1.6, the left side is infarcted. Further, the outputted infarct judgment outcome is corrected as such: correcting 18: [1, 0.95, −1.6] to 18: [0, 0.95, −1.6], while the remained infarct judgment outcomes do not change; then, the corrected infarct judgment outcomes serve as updated infarct judgment outcomes for subsequent grading.

In an embodiment of the present disclosure, the outputted infarct judgment outcomes are subjected to further judgment based on the confidence algorithm combining the ratio algorithm and the difference algorithm. This approach uses the function c=(ratio−0.5)/0.7+(diff+20)/50 to compute the c values of the outputted infarct judgment outcomes. The lower the c value, the higher the probability of infarct onset, i.e., the higher the confidence; by comparing the smallest c values of bilateral target areas, the side with the lower smallest c value is infarcted. The c values of the target areas are computed based on the infarct judgment outcomes outputted in the embodiment of FIG. 6 using the ratio algorithm or the difference algorithm; then the c values of the target areas 1-20 are consecutively: 1.09, 0.95, 0.97, 1.11, 1.13, 1.17, 1.09, 1.15, 1.30, 1.28, 1.11, 1.10, 1.05, 1.14, 1.22, 1.11, 1.11, 1.01, 1.11, 1.11; based on the outcomes of the c values, it is seen that the smallest c value at the left side is 0.95, while the smallest c value at the right side is 1.01; because 0.95<1.01, the left side is infarcted. Further, the outputted infarct judgment outcome is corrected as such: correcting 18: [1, 0.95, −1.6] to 18: [0, 0.95, −1.6], while the remained infarct judgment outcomes do not change; then, the corrected infarct judgment outcomes serve as updated infarct judgment outcomes for subsequent grading.

If the infarct judgment outcomes outputted by step S407 show that one side is infarcted, then it is unnecessary to perform further judgment, and the infarct judgment outcomes may be directly used in subsequent grading.

Step S413: outputting a grading outcome based on infarct judgment outcomes regarding all target areas in the left and right cerebral hemispheres.

Based on the infarct judgment outcomes regarding all target areas in the left and right cerebral hemispheres outputted in step S411, wherein the weight of each target area is 1 point and the total points is 10 points, by subtracting the number of infarcted target areas from the 10 points, the resulting value is the grading outcome. Specifically, the target areas 1-20 are traversed to screen, from the outputted infarct judgment outcomes, arrays whose first element is 1, and the number as counted is the number of infarcted target areas. In grading, 1 point is deducted for each infarcted target area; the finally obtained number is the grading outcome.

In an embodiment of the present disclosure, an outputted grading outcome may be an ASPECTS value, which is a result obtained based on performing infarct judgments twice on the target areas in the left and right cerebral hemispheres. The outputted grading outcome may also be two ASPECTS values, respectively representing the ASPECTS values of the left and right cerebral hemispheres. If the grading outcome is represented by two ASPECTS values, in a specific application, the grading outcome for the corresponding side may be directly outputted based on the infarcted side determined with a known symptom, without a need of performing infarct judgments twice on the target areas in the left and right cerebral hemispheres. If the known symptom exhibits left hemiplegia, it is seen that the right cerebral hemisphere is infarcted; then during grading, the grading outcome regarding the right cerebral hemisphere may be directly outputted.

The cranial CT-based grading method for anterior circulation may also be applied to posterior circulation. In the specific implementation process, the cranial CT-based grading method for posterior circulation has somewhat differences from that for the anterior circulation. For example, the target areas for posterior circulation are: pons, bilateral cerebella, midbrain, bilateral thalami, and bilateral PCA-territories, and the digital labels are: 0 representing background, 1 representing pons, 2 representing left cerebellum, 3 representing right cerebellum, 4 representing midbrain, 5 representing left thalamus, 6 representing right thalamus, 7 representing left PCA-territory, and 8 representing right PCA-territory. The features as extracted during extracting target areas are also different from those for the anterior circulation. Because in posterior-circulation target areas, not all areas are present in both left and right cerebral hemispheres, e.g., the pons and the midbrain need not be subjected to bilateral infarct judgment, the infarct judgment is also performed differently from that for the anterior circulation. Besides, in posterior circulation grading, the weights of respective target areas also differ from the anterior circulation. Specifically, for posterior-circulation ASPECTS assessment, the weights of the pons and the midbrain are 2, while the weights of remained areas are all 1.

Irrespective of grading anterior circulation or posterior circulation, all ideas based on the written description of the present disclosure or all improved methods proposed based on the present disclosure fall within the protection scope of the present disclosure.

What have been elaborated above is a cranial CT-based grading method; correspondingly, the present disclosure further provides a cranial CT-based grading system, as shown in FIG. 7, which specifically comprises:

an area extracting module configured for extracting target areas from to-be-processed multi-frame cranial CT data, wherein the target areas refer to areas for being graded in the cranial CT data;

an infarct identifying module configured for performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area; and

a grading module configured for outputting a grading outcome based on infarct judgment outcomes regarding all target areas.

What have been described above are preferred embodiments of the present disclosure.

The other embodiments fall within the scope of the appended claims. In some cases, the actions or steps disclosed in the claims may be executed according to a sequence different from those disclosed in the embodiments but may still achieve a desired result. Additionally, it is not compulsory for to follow the specific sequence or continuous sequence as illustrated in the drawings to achieve the desired result. In some embodiments, multi-task processing or concurrent processing is optional or likely beneficial.

Respective embodiments in the specification are described in a progressive manner, and same or similar parts between various embodiments may be referenced to each other, while each embodiment focuses on differences from other embodiments. Particularly, for an apparatus embodiment, an electronic device embodiment, and a non-volatile computer storage medium embodiment, because they are basically similar to the method embodiments, they are not detailed here and may refer to the depictions in the corresponding method embodiments.

The apparatus, electronic device, and non-volatile computer storage medium provided in the embodiments of the present disclosure correspond to the method; therefore, the apparatus, electronic device, and non-volatile computer storage medium also have beneficial effects of the corresponding method. As the beneficial effects of the method have been illustrated in detail, they will not be detailed here.

In 1990s, improvement of a technology may be apparently differentiated into hardware improvement (e.g., improvement of a circuit structure of a diode, a transistor, a switch, etc.) or software improvement (e.g., improvement of a method process). However, with development of technology, currently improvement of many method processes may be regarded as direct improvement to a hardware circuit structure. Designers always program an improved method process into a hardware circuit to obtain a corresponding hardware circuit structure. Therefore, it is improper to allege that improvement of a method process cannot be implemented by a hardware entity module. For example, a programmable logic device (PLD) (such as a field programmable gate array FPGA) is such an integrated circuit, a logic function of which is determined by programming a corresponding device. A designer may integrate a digital system on a piece of PLD by programming, without a need of engaging a chip manufacturer to design and fabricate a dedicated integrated circuit chip. Moreover, currently, in replacement of manual fabrication of an integrated circuit chip, this programming is mostly implemented by a logic compiler, which is similar to a software compiler used when developing and writing a program. To compile the previous original code, a specific programming language is needed, which is referred to as a hardware description language (HDL). Further, there are more than one HDLs, e.g., ABEL (Advanced Boolean Expression Language), AHDL(Altera Hardware Description Language), Confluence, CUPL (Cornell University Programming Language), HDCal, JHDL (Java Hardware Description Language), Lava, Lola, MyHDL, PALASM, RHDL (Ruby Hardware Description Language), among which, VHDL (Very-High-Speed Integrated Circuit Hardware Description Language) and Verilog are used most prevalently. Those skilled in the art should also understand that a hardware circuit for a logic method process can be easily implemented by subjecting, without much efforts, the method process to logic programming using the above hardware descriptive languages into an integrated circuit.

A controller may be implemented according to any appropriate manner. For example, the controller may adopt manners such as a microprocessor or processor and a computer readable medium storing computer readable program codes (e.g., software or firmware) executable by the (micro) processor, a logic gate, a switch, an application specific integrated circuit (ASIC), a programmable logic controller, and an inlaid microcontroller. Examples of the controller include, but are not limited to, the following microcontrollers: ARC 625D,

Atmel AT91SAM, Microchip PIC18F26K20 and Silicone Labs C8051F320. The memory controller may also be implemented as part of the control logic of the memory. Those skilled in the art may further understand that besides implementing the controller by pure computer readable program codes, the method steps may be surely subjected to logic programming to enable the controller to implement the same functions in forms of a logic gate, a switch, an ASIC, a programmable logic controller, and an inlaid microcontroller, etc. Therefore, the controller may be regarded as a hardware component, while the modules for implementing various functions included therein may also be regarded as the structures inside the hardware component. Or, the modules for implementing various functions may be regarded as software modules for implementing the method or structures inside the hardware component.

The system, apparatus, module or unit illustrated by the embodiments above may be implemented by a computer chip or entity, or implemented by a product having a certain function. A typical implementation device is a computer. Specifically, the computer for example may be a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media device, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

To facilitate description, the apparatuses above are partitioned into various units by functions to describe. Of course, when implementing one or more embodiments of the present application, functions of various units may be implemented in one or more pieces of software and/or hardware.

Those skilled in the art should understand that the embodiments of the present disclosure may be provided as a method, a system, or a computer program product. Therefore, the embodiments of the present disclosure may adopt a form of complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the embodiments of the present disclosure may adopt a form of a computer program product implemented on one or more computer-adaptable storage media including computer-adaptable program code (including, but not limited to, a magnetic disc memory, CD-ROM, and optical memory, etc.).

The present disclosure is described with reference to the flow diagram and/or block diagram of the method, apparatus (system) and computer program product according to the embodiments of the present disclosure. It needs to be noted that each flow and/or block in the flow diagram and/or block diagram, and a combination of the flow and/or block in the flow diagram and/or block diagram, may be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general-purpose computer, a dedicated computer, an embedded processor, or other programmable data processing device to generate a machine, such that an apparatus for implementing the functions specified in one or more flows of the flow diagram and/or one or more blocks in the block diagram is implemented via the computer or the processor of other programmable data processing device.

These computer program instructions may also be stored in a computer readable memory that may boot the computer or other programmable data processing device to work in a specific manner such that the instructions stored in the computer readable memory to produce a product including an instruction apparatus, the instruction apparatus implementing the functions specified in one or more flows of the flow diagram and/or in one or more blocks in the block diagram.

These computer program instructions may be loaded on the computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a processing implemented by the computer, such that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more flows of the flow diagram and/or one or more blocks in the block diagram is implemented via the computer or the processor of other programmable data processing device.

In a typical configuration, the computing device includes one or more processors (CPUs), an input/output interface, a network interface, and a memory.

The memory may include a non-permanent memory in a computer readable medium, a random-access memory (RAM) and/or a non-volatile memory, e.g., a read-only memory

(ROM) or a flash memory (flash RAM). The memory is an example of a computer readable medium.

The computer readable memory includes a permanent type, non-permanent type, a mobile type, and a non-mobile type, which may implement information storage by any method or technology. The information may be a computer-readable instruction, a data structure, a module of a program or other data. Examples of the memory mediums of the computer include, but are not limited to, a phase-change RAM (PRAM), a static random access memory (SRAM), a dynamic random access memory (DRAM), other type of random access memory (RAM), a read-only memory (ROM), an electrically erasable programmable read only memory (EEPROM), a flash memory body or other memory technology, a CD-ROM (Compact Disc Read-Only Memory), a digital multi-function optical disc (DVD) or other optical memory, a magnetic cassette type magnetic tape, a magnetic tape disc memory, or other magnetic storage device or any other non-transmission medium which may be configured for storing information to be accessed by a computing device. Based on the definitions in the specification, the computer readable medium does not include a transitory media, e.g., a modulated data signal and a carrier.

It needs also be noted that the terms “include,” “comprise” or any other variables intend for a non-exclusive inclusion, such that a process, a method, a product or a system including a series of elements not only includes those elements, but also includes other elements that are not explicitly specified or further includes the elements inherent in the process, method, product or system. Without more restrictions, an element limited by the phase “including one . . . ” does not exclude a presence of further equivalent elements in the process, method, product or system including the elements.

The present application may be described in a general context of the computer-executable instruction executed by the computer, for example, a program module. Generally, the program module includes a routine, a program, an object, a component, and a data structure, etc., which executes a specific task or implements a specific abstract data type.

The present application may be practiced in a distributed computing environment, in which a task is performed by a remote processing device connected via a communication network. In the distributed computing environment, the program module may be located on a local or remote computer storage medium, including the memory device.

Respective embodiments in the specification are described in a progressive manner, and same or similar parts between various embodiments may be referenced to each other, while each embodiment focuses on differences from other embodiments. Particularly, for a system embodiment, because it is substantially similar to the method embodiment, it is described relatively simply. Relevant parts may refer to the method embodiments.

What have been described above are only preferred embodiments of the present disclosure, not for limiting the present disclosure; to those skilled in the art, the present disclosure may have various alterations and changes. Any modifications, equivalent substitutions, and improvements within the spirit and principle of the present disclosure should be included within the protection scope of the present disclosure. 

1. A cranial CT-based grading method, comprising: determining frames where target image slices are located from to-be-processed multi-frame cranial CT data, wherein the target image slices refer to the slices, where the cranial CT data for being graded are located, in the cranial CT; extracting target areas based on the frames where the target image slices are located, wherein the target areas refer to areas for being graded in the cranial CT data; performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area; and outputting a grading outcome based on infarct judgment outcomes regarding all target areas.
 2. The method according to claim 1, wherein the determining frames where target image slices are located from to-be-processed multi-frame cranial CT data specifically comprises: extracting image features of the to-be-processed multi-frame cranial CT data, and determining distances from respective frames of cranial CT data in the multi-frame cranial CT data to respective target image slices; and determining the frames where the target image slices are located based on the distances from the respective frames of cranial CT data to the respective target image slices.
 3. The method according to claim 1, wherein the extracting target areas based on the frames where the target image slices are located specifically comprises: classifying each pixel point in the cranial CT data using digital labels based on the frames where the target image slices are located and outputting a two-dimensional matrix with digital labels corresponding to respective pixel points in the frames where the target image slices are located, wherein the digital labels are in one-to-one correspondence with the target areas, and the two-dimensional matrix is in correspondence with the frames where the target image slices are located.
 4. The method according to claim 1, wherein the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area specifically comprises: performing infarct judgment on each pixel point included in the target area to output an infarct judgment outcome regarding the target area.
 5. The method according to claim 1, wherein the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area further comprises: judging, based on the infarct judgment outcome regarding the target area, whether infarct is indicated in the target areas in both left and right cerebral hemispheres; and if infarct is indicated in the target areas in both left and right cerebral hemispheres, further determining which specific side is infarcted, and correcting the infarct judgment outcome regarding the target area as an update infarct judgment outcome regarding the target area.
 6. The method according to claim 1, wherein the outputting a grading outcome based on infarct judgment outcomes regarding all target areas specifically comprises: determining all infarcted target areas based on the infarct judgment outcomes regarding all target areas; subtracting, based on weights allotted to respective target areas, weights of the infarcted target areas from the total score to output a resulting value as the grading outcome.
 7. A cranial CT-based grading system, comprising: an area extracting module configured for extracting target areas from to-be-processed multi-frame cranial CT data, wherein the target areas refer to areas for being graded in the cranial CT data; an infarct identifying module configured for performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area; and a grading module configured for outputting a grading outcome based on infarct judgment outcomes regarding all target areas.
 8. The system according to claim 7, wherein the extracting target areas from to-be-processed multi-frame cranial CT data specifically comprises: determining frames where target image slices are located from the to-be-processed multi-frame cranial CT data, wherein the target image slices refer to the slices, where the cranial CT data for being graded are located, in the cranial CT; and extracting the target areas based on the frames where the target image slices are located, wherein the target areas refer to areas for being graded in the cranial CT data.
 9. The system according to claim 8, wherein the determining frames where target image slices are located from the to-be-processed multi-frame cranial CT data specifically comprises: extracting image features of the to-be-processed multi-frame cranial CT data, and determining distances from respective frames of cranial CT data in the multi-frame cranial CT data to respective target image slices; and determining the frames where the target image slices are located based on the distances from the respective frames of cranial CT data to the respective target image slices.
 10. The system according to claim 8, wherein the extracting the target areas based on the frames where the target image slices are located specifically comprises: classifying each pixel point in the cranial CT data using digital labels based on the frames where the target image slices are located and outputting a two-dimensional matrix with digital labels corresponding to respective pixel points in the frames where the target image slices are located, wherein the digital labels are in one-to-one correspondence with the target areas, and the two-dimensional matrix is in correspondence with the frames where the target image slices are located.
 11. The system according to claim 7, wherein the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area specifically comprises: performing infarct judgment on each pixel point included in the target area to output an infarct judgment outcome regarding the target area.
 12. The system according to claim 7, wherein the performing infarct judgment on each target area included in the target areas to output an infarct judgment outcome regarding the target area further comprises: judging, based on the infarct judgment outcome regarding the target area, whether infarct is indicated in the target areas in both left and right cerebral hemispheres; and if infarct is indicated in the target areas in both left and right cerebral hemispheres, further determining which specific side is infarcted, and correcting the infarct judgment outcome regarding the target area as an update infarct judgment outcome regarding the target area.
 13. The system according to claim 7, wherein the outputting a grading outcome based on infarct judgment outcomes regarding all target areas specifically comprises: determining all infarcted target areas based on the infarct judgment outcomes regarding all target areas; and subtracting, based on weights allotted to respective target areas, weights of the infarcted target areas from the total score to output a resulting value as the grading outcome. 